The proposed investigation will utilize the animal model of endolymphatic hydrops to study inner ear fluid pressure regulation and the resulting effects on vestibular function. The hypothesis of this research is that alteration in endolymphatic and perilymphatic pressure regulation is fundamental to the development of endolymphatic hydrops and that this imbalance can result in vestibular dysfunction. Two projects are proposed to test this hypothesis. Vestibular function in animals with surgically induced unilateral endolymphatic hydrops will be quantified and compared to animals with normal and sham-operated ears. Vestibulo-ocular, visual vestibulo-ocular and optokinetic measurements will be determined. A morphologic correlation will be made between vestibular function and severity of hydrops. Additionally, postural inversion and administration of a hyperosmolar diuretic will be individually used as a means to alter intralabyrinthine pressure and possibly vestibular function. Endolymph and perilymph pressures will be measured in animals with normal and hydropic inner ears under experimental conditions that modulate these pressures. These pressures will be measured in the hydropic labyrinth with reference to the time frame in which hydrops develops. A morphologic correlation will be made between these measurements and the severity of hydrops. The interaction of perilymph and endolymph pressure in both normal and hydrops ears will be studied in relation to variables that can possibly influence these pressures including intracranial, central venous and middle ear pressures and the compliance of the membranous labyrinth. The individual effects of postural inversion and the administration of a hyperosmolar diuretic on the inner ear fluid pressures will also be determined. A mathematical model will be produced of the anatomic and physiologic variables that influence and determine endolymph and perilymph pressure for both the normal and hydrops ear.